The photocatalytic decomposition of chloroform by tetrachloroaurate(III)

Near-UV irradiation of solutions of (Bu 4 N)AuCl 4 in aerated ethanol-stabilized chloroform causes the continuous decomposition of chloroform, as evidenced by the production of many equivalents of HCl and peroxides. At the outset of irradiation, most of the AuCl 4 − is reduced to AuCl 2 − , but the reduction stops and is reversed. The same experiments done in ethanol-free chloroform cause chloroform decomposition only until the irreversible reduction of the gold is complete. In deoxygenated ethanol-free chloroform, irreversible reduction to AuCl 2 − is accompanied by the formation of HCl and CCl 4 , while the main decomposition products in deoxygenated ethanol-stabilized chloroform are HCl and C 2 Cl 6 . It is proposed that, in ethanol-free chloroform, photoreduction of AuCl 4 − begins with the concerted elimination of HCl from an association complex of CHCl 3 with AuCl 4 − , and that ethanol suppresses complex formation, leaving a slower radical process to carry out the photoreduction of AuCl 4 − in ethanol-stabilized chloroform. In the presence of oxygen, the radical process causes a build-up of CCl 3 OOH, which reoxidizes AuCl 2 − to AuCl 4 − and allows the photodecomposition of CHCl 3 to continue indefinitely. Graphical Abstract